# EM waves and forces

1. Feb 16, 2014

### VishalChauhan

Would a particle kept in the path of an electromagnetic wave experience a force?
Both magnetic and electric field are present, so the equation of motion may be complex, but i have never seen my textbook refer to the the possibility of an em wave causing a charged particle to move.

2. Feb 16, 2014

Staff Emeritus
EM waves cause particles to move all the time. That's how a radio antenna works - the radio wave causes the electrons in the antenna to move, which produces a current, which is detected by the radio receiver.

3. Feb 16, 2014

### VishalChauhan

So if a charged particle is kept in a ray of light, would it begin to accelerate?

4. Feb 16, 2014

Staff Emeritus
I'm not sure what you mean by "kept in a ray of light", but yes, the EM field of light can accelerate charges.

5. Feb 16, 2014

### kindlin

Well of course a light wave can accelerate a charged particle, an EM wave has the M part in it, which would affect a charged particle.

What I've always wondered is, if you had, say, an atom of silicon floating in space and a stream of photons came flying at it, a few photons would hit the silicon atom. Would these collisions cause the silicon atom to move?

I know a photon is massless, so conservation of momentum says no, but it also has a lot of energy attached to it (doesn't it?) so from E=mc^2, shouldn't it be able to impart some force?

6. Feb 16, 2014

### nasu

The photon has momentum even though it's massless. So there is no contradiction. Conservation of momentum does not say "no".

But I think you should start a new topic, as you bring a different question.